This invention relates to a novel method and apparatus for the treatment of tear-related disorders of the eye. More specifically, this invention relates to a punctum plug for treating cases of mild to moderate keratitis sicca or kertoconjunctivitis sicca (dry eye) and related disorders by occluding the flow of lacrimal fluid into the punctum and canaliculus.
In a healthy eye, movement of the upper eyelid spreads a film of tears over the corneal and conjunctival epithelia, making the eye smooth and optically clear. The tear film is composed of three layers which coat the surface of the eye. An outer, oily layer is produced by small glands called meibomian glands located at the edges of the eyelids. This outer layer provides a smooth tear surface and reduces evaporation of tears. An intermediate, watery layer is produced by a large lacrimal gland and a plurality of small glands scattered throughout the conjunctiva. This watery layer contains the largest amount of fluid and cleanses the eye by washing away foreign particles and irritants. An inner layer consists of mucus produced by goblet cells in the conjunctiva. This inner layer allows the watery layer to spread evenly over the surface of the eye. In addition, the mucus produced by the goblet cells enables the aqueous tears to wet the epithelial surface.
Normally, the preocular tear film (PTF) is formed by the cooperative interaction of products from the Meibomian glands, the lacrimal gland, and the goblet cells; however, sometimes these glands produce less than adequate amounts of tears, resulting in dry eye.
Dry eye is characterized by an inability to maintain a stable preocular tear film due to insufficient production or excessive drainage of lacrimal fluid. Dry eye describes a continuum of problems which range from discomfort, to decreased vision and pain, and, in extreme cases, to blindness. The causes of dry eye include aging, disease inflammatory processes, and prescription drug side effects.
A previous prior art practice in treating dry eye has been to utilize various types of topical drops and ointments. Some sufferers of dry eye prefer using humidifiers and vaporizers to increase the moisture level in the surrounding air, which helps by decreasing evaporation of lacrimal fluid from the eye.
More recently, permanent punctal occlusion has proven to be an effective method of treating tear-related disorders including dry eye, corneal ulcers, conjunctivitis, blepharitis, contact lens problems and other external eye diseases. In extreme cases of discomfort and pain, such as occur in Sjogren's syndrome, permanent closure of the puncta and canaliculi by surgery or cauterization has produced marked success.
Each of the aforementioned treatments, however, possess certain inherent limitations. Topical drops and ointments require frequent re-applications. Humidifiers and vaporizers are relatively bulky and must be connected to an electrical source and, thus, are not satisfactory for all occasions, such as outdoor activities. Finally, surgical or cauterization procedures are costly and create a danger of subsequent epiphora and/or infection, the destruction of normal tissue requires surgical intervention to reverse.
The foregoing noted problems of mild to moderate dry eye have been advantageously addressed by the introduction of a punctum plug which provides reversible punctal occlusion as disclosed and claimed in the previously identified Freeman U.S. Pat. No. 3,949,750. The disclosure of this patent is incorporated herein by reference as though set forth at length.
Total occlusion of a punctum with a silicone plug of the Freeman design has proved to be very beneficial to patients suffering from dry eye conditions. However, some physicians have reported that insertion of the punctum plug is occasionally difficult because of the size of the plug relative to the size of a patient's punctal opening. In this connection it is often necessary to dilate a patient's punctum for plug insertion which may cause patient anxiety and/or discomfort.
The use of polyhydroxyethylmethacrylate p(HEMA) as a plug composition has been theorized, at least in part, because in a dry state its firmness facilitates the process of insertion. Once inserted, HEMA is hydrated, becomes soft and flexible and swells to conform in shape to a patient's lacrimal duct, or canaliculus, thereby improving the closure of the punctal aperture. However, the biocompatibility of HEMA, a solid hydrogel material, has not been satisfactory. It has been determined that soluble proteinaceous substances present in the preocular tear film (PTF) and canaliculus may be absorbed into or adsorbed onto the hydrogel and denatured proteins can initiate immune responses.
The difficulties in the preceding are not intended to be exhaustive but rather are among many which may tend to reduce the effectiveness of prior known methods and devices for treatment of dry eye. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that methods and devices for treating dry eye syndrome appearing in the past will admit to worthwhile improvement.